Abstract

The effect
of monovalent cations (Li+, K+, NH4+,
Na+)
on the water structure in aqueous chloride and acetate solutions was
characterized by oxygen K-edge X-ray absorption spectroscopy(XAS),X-ray emission
spectroscopy, and resonant inelastic X-ray scattering (RIXS) of a liquid microjet. We show ion-
and counterion dependent effects on the emission spectra of the oxygen K-edge, which we
attribute to modifications of the hydrogen bond network of water. For acetates, ion pairing with
carboxylates was also probed selectively by XAS and RIXS. We correlate our experimental results to
speciation data and to the salting-out properties of the cations.

Received 26 March 2014Accepted 10 June 2014Published online 18 June 2014

Acknowledgments:

This work was supported by the Helmholtz-Gemeinschaft via the young investigator fund
VH-NG-635 and the European Research Council Grant No. 279344. K.M.L. is grateful to the
financial support by the Helmholtz Postdoc Grant PD-059. T.P. would like to acknowledge the
Alexander von Humboldt Foundation for financial support.

Abstract

The effect
of monovalent cations (Li+, K+, NH4+,
Na+)
on the water structure in aqueous chloride and acetate solutions was
characterized by oxygen K-edge X-ray absorption spectroscopy(XAS),X-ray emission
spectroscopy, and resonant inelastic X-ray scattering (RIXS) of a liquid microjet. We show ion-
and counterion dependent effects on the emission spectra of the oxygen K-edge, which we
attribute to modifications of the hydrogen bond network of water. For acetates, ion pairing with
carboxylates was also probed selectively by XAS and RIXS. We correlate our experimental results to
speciation data and to the salting-out properties of the cations.